Idiopathic thrombocytopenic purpura appears to result from an immunologic reaction against a platelet associated antigen(s) with subsequent production of an antiplatelet antibody. The present proposal describes a comprehensive approach for evaluating patients with immune thrombocytopenia. The presence of a platelet or megakaryocyte "autoantigen" will be evaluated by determining leukocyte blastogenesis in the presence of autologous platelets or megakaryocytes. Ig production by leukocytes from four lymphoid areas in ITP patients (spleen, bone marrow, lymph nodes, and blood) will be quantitated using the Fab-anti Fab Ig assay system and copmapre to data from control subjects. Antiplatelet reactivity of autologous sera, lymphoid organ eluates and Ig produced in culture will be evaluated in vitro using three assay systems: platelet Ig bindin, platelet factor 3 release and platelet phagocytosis, as well as, in vivo using two means of evaluation: controlled transfusion of autologous plasma or culture Ig and autologous platelet survival after invitro incubation with plasma or culture Ig. Concurrent study of MIF production will be performed to determine the role of cell-mediated immunity in these diseases. These experimental data will be correlated with the patients' clinical course and therapeutic status. A similr experimental approach will be employed in studying the secondary immune purpuras.